Income tax returns are due this week. And the Senate chose this week to take up a proposal that millionaires should pay a minimum tax. It's President Obama's so-called Buffett Rule. The rules of the Senate make it unlikely this measure will pass, but Democrats are eager to force a vote on it. Consider this an early shot in the general election campaign, now that most of Mitt Romney's rivals for the Republican nomination have dropped away.

Joining us now to talk about this, as she does most Mondays, is commentator Cokie Roberts. Cokie, good morning.

COKIE ROBERTS, BYLINE: Hi, Steve.

INSKEEP: OK, Rick Santorum is out. Mitt Romney is still standing. Do you see his campaign changing as he aims more at President Obama?

ROBERTS: Sure. Not only is he aiming at Obama but he's aiming toward certain voters. We saw last week this swing toward women, trying to close that gender gap. And Republicans tend to do well with married women. And Hilary Rosen, the Democratic consultant, gave him a gift in her off comment about Ann Romney never having worked a day in her life.

We're also getting reports that Romney is getting specific about what kinds of tax reform he would do, that he would say that high earners can't deduct the mortgage for a second home - that kind of thing. So you know, going more toward the middle there, trying to get some of the voters that Obama is getting on this issue of fairness.

INSKEEP: And I suppose President Obama is trying not to be painted as a particular kind of candidate. And you see the president responding very quickly when Mitt Romney gave a speech to the National Rifle Association.

ROBERTS: Well, that's the thing we're really seeing, Steve, is - I was talking to a Republican consultant over the weekend who said the difference between this and 2004 is like horse and buggy versus jet travel. I mean everything is just immediate. And we saw that with the Hilary Rosen/Ann Romney thing, with Ann Romney tweeting right away and then the entire Obama campaign, followed by the president himself, responding.

And the same thing - Mitt Romney went to the NRA and made a very strong speech, and immediately President Obama's campaign had a response up. So that's what we're going to see from now until November.

INSKEEP: You allude to 2004, of course, that's the last time that an incumbent president was running for re-election. Now, the economy always is so huge in these elections. And what does the current state of economy tell us about this fall?

ROBERTS: Well, it is incredibly huge. What the economists and political scientists tell us is that from here on out is when the voters really pay attention to their economic well-being. Anything that's happened for the last few years really doesn't signify - it's from April to November of an election year. And right now things are a little bit rocky.

You know, the unemployment numbers, the people going for claims ticked back up last week. The market is quite shaky because of what's going on in Europe. And what we're seeing in the polls is that people who are feeling like we are coming out of a recession and things are good are going for President Obama by huge numbers - two-thirds in the most recent ABC/Washington Post poll.

But people who say that we're still in a recession, only 35 percent of them are saying that they are with President Obama. So he has really got to convince people that this recession is over. And that's going to be hard to do, given the way the economy is just sort of rocking back and forth these days.

INSKEEP: One other thing, very briefly. Does it affect the president at all that he goes to Latin America, on a trip that's supposed to be about drumming up economic growth, and it's overshadowed by a scandal involving Secret Service agents?

ROBERTS: I don't think that it has any long-term effect or any real political effect. It's just, as you say, it overshadowed what he wanted to get out, which was a message about trade and economic growth. And also an appeal to Hispanics, a very important voter group in his upcoming election.